Planets in the Solar System

For eons, men have gazed towards the skies in awe and wonder, the same way digableplanets.org has. Slowly but surely, science has unraveled the mysteries of our solar system, correcting many misconceptions along the way. For example, it was during the 16th century an on that the notion of a stationary Earth was first dispelled by Nicolaus Copernicus, and even today long established concepts are examined under a new light. For instance, Pluto was recently reclassified from a full-on planet to the the largest dwarf planet in the solar system, but more on that later here at digableplanets.org.

Our solar system is broadly divided in inner planets and outer planets. Inner, or terrestrial, planets are those composed mainly of rocks and/or metals, and are the ones closer to the Sun, namely Mercury, Venus, Earth and Mars. Furthermore, these planets have few or no moons, and do not have ring systems. Inner and outer planets are separated by an asteroid belt between Mars and Jupiter. Outer planets (Jupiter. Saturn, Uranus and Neptune), also known as gas giants, are made up mainly of helium and hydrogen, as well as ice in the case of Uranus and Neptune. All of them have many satellites and ring systems, although Saturn's is the only one that can be seen from Earth.

Going back to the dwarf planets mentioned before, these are spherical celestial bodies which orbit around the sun but are not gravitationally dominant, in other words, they share their orbit with other bodies, as is the case of Pluto sharing its orbit with objects in the Kuiper belt. The International Astronomical Union recognizes four other dwarf planets, Ceres, Haumea, Makemake, and Eris. Ceres is in the asteroid belt and was discovered in 1801 by Giuseppe Piazzi. Haumea, Makemake, and Eris are all in the Kuiper Belt and were discovered between 2004 and 2005. There are still several candidates to be categorized as dwarf planets, including Sedna, Orcus, Quaoar, Vesta, Ixion, Varuna, and others.

However, as varied as are own solar system is, there so much more beyond. Just outside of it is the aforementioned Kuiper Belt, similar to the asteroid belt but larger and more massive, and comprised of frozen volatiles. The entirety of the solar system is located in the Milky Way, which is a spiral galaxy containing anywhere from 200 to 400 billion stars, and at least 50 billion planets. As large as this sounds, the Milky Way is only part of a local group of galaxies and is itself located in a supercluster which also includes the Virgo cluster of galaxies. The observable Universe alone has approximately 200 billion galaxies. There is a lot to be learned out there, and hopefully some of it will be found at digableplanets.org.